Evaluation of implant alignment in navigated unicompartmental knee arthroplasty: a comparison of 2D and 3D imaging

This study aimed to compare two-dimensional (2D) and three-dimensional (3D) methods for evaluating implant alignment in navigated UKA. Nineteen UKAs in 18 subjects (7 men) were performed using an image-free navigation system. Coronal and sagittal implant alignments were assessed using radiographs (2D evaluation) and 3D image-matching software. The accuracy of 2D evaluation was compared with that of 3D evaluation. A deviation > 3° from the 3D evaluation was defined as an outlier. In the 2D evaluation, outliers for the femoral component were observed in both the coronal plane (6/19 subjects) and the sagittal plane (3/19 subjects). In UKA, assessment of the implant position might be misjudged because of the design of the implant, especially for the femoral component; 3D methods are ideal for assessment of implant alignment.